As a thin, high image quality, and low power consumption display device, an organic EL (Electro Luminescence) display is known. The organic EL display includes a plurality of pixel circuits including an organic EL element and a driving transistor. When providing display on the organic EL display, there is a need to compensate for variations in the threshold voltage of the driving transistors and an increase in resistance caused by deterioration over time of the organic EL elements.
Various types of pixel circuits that perform compensation operation are conventionally known. Patent Document 1 describes a pixel circuit 80 shown in FIG. 18. The pixel circuit 80 includes TFTs (Thin Film Transistors) 81 to 85, a capacitor 86, and an organic EL element 87. When writing to the pixel circuit 80, first, the TFTs 82 and 84 are controlled to an on state to initialize the gate-source voltage of the TFT 85 (driving transistor). Then, the TFT 84 and the TFT 83 are controlled to an off state in turn to allow the capacitor 86 to hold the threshold voltage of the TFT 85. Then, a data potential is applied to a data line DTL and the TFT 81 is controlled to an on state. Accordingly, variations in the threshold voltage of the TFT 85 and an increase in resistance caused by deterioration over time of the organic EL element 87 can be compensated for.
The pixel circuit 80 is connected to the data line DTL, four control lines WSL, AZL1, AZL2, and DSL, and three power lines (a wiring line for Vofs, a wiring line for Vcc, and a wiring line for Vss). In general, the larger the number of wiring lines (particularly, control lines) connected to a pixel circuit, the more complex the circuit becomes, increasing manufacturing cost. Hence, Patent Document 1 describes a pixel circuit where the source terminal of the TFT 82 or the TFT 84 is connected to the control line WSL. Patent Document 2 describes a pixel circuit where the gate terminal of the TFT 82 is connected to a control line WSL in a previous row. By thus commonizing a control line and a power line, the number of wiring lines can be reduced.
Patent Document 3 describes a pixel circuit 90 shown in FIG. 19. The pixel circuit 90 includes TFTs 91 and 92, a capacitor 93, and an organic EL element 94. When writing to the pixel circuit 90, first, the TFT 91 is controlled to an on state. Then, an initialization potential is applied to a power line DSL to provide the initialization potential to the anode terminal of the organic EL element 94. Then, a power supply potential is applied to the power line DSL to allow the capacitor 93 to hold the threshold voltage of the TFT 92 (driving transistor). Then, a data potential is applied to a data line DTL. By thus providing an initialization potential from the power line, variations in the threshold voltage of the TFT 92 can be compensated for with a small number of elements. Patent Document 4 describes a pixel circuit where an initialization potential is provided from a power line and a reference potential is provided from a data line. Patent Document 5 describes a pixel circuit that performs compensation operation during a plurality of horizontal periods before writing.